It is widely known that electronic parts such as semiconductor packages generate heat in use, thereby lowering the performance thereof. To solve this problem, various heat dissipating techniques have been used. One typical method is to provide a cooling member such as a heat spreader in the vicinity of a heat-generating part and bring them into close contact to effectively remove heat through the cooling member.
In this case, if there is a space between the heat-generating member and the cooling member, thermal conduction does not proceed smoothly because of the presence of air, which is poor in heat conductivity, and therefore, the temperature of the heat-generating member cannot be sufficiently reduced. To prevent such phenomena, there have been conventionally used, for the purpose of preventing the presence of air, heat-dissipating greases or heat-dissipating sheets that have good heat conductivity and followability to the surface of the member (Patent Literatures 1 to 11).
A thin and compressible heat-dissipating grease is suitable for measures against heat of semiconductor packages in view of heat-dissipating performance. Particularly, it is preferable, in view of reliability, to use a thermosetting heat-dissipating grease that hardly causes outflow of the grease (pumping out) due to the thermal history between heating and cooling of the heat-generating part. On the other hand, since extremely high terminal-density and a reduction in mounting area are required for semiconductor packages in recent years, a manner in which a package is connected to a substrate after a reflow process for fusing solder applied to the bottom of the package at a high temperature of 200° C. or higher, is most often used instead of the conventional manner of connecting a package and a substrate through a lead frame. However, the reflow process of subjecting to high temperature of 200° C. or higher extremely accelerates curing of the thermosetting heat-dissipating grease. Therefore, the heat-dissipating grease cannot be compressed into a prescribed thickness, and the applied heat-dissipating grease cannot sufficiently spread over the whole heat-generating part. Thus, there is a problem of insufficient heat-dissipating performance.